The veteran Red Cross aid worker from says the disaster is the worst he has seen when it comes to loss of assets and the number of people hit. "You've got to be careful comparing disasters but the affected population here is huge," he says. "It's just incredible."

The Age accompanied Mr Handby, a water and sanitation specialist, as he travelled with a Red Cross and Red Crescent assessment team to flood-hit areas along the Kabul River in Khyber Pakhtunkhwa province (formerly North-West Frontier Province).

Damage to crops, roads and bridges has caused food prices to triple in some parts of the country, adding to the pain of the 14 million people affected by one of the worst natural disasters to hit the poor nation.

About 1500 people have died, and the UN estimates up to 7 million people need emergency assistance.

In some places plastic bags and other debris are stuck in tangled overhead electric wires, revealing the terrifying height reached by the floodwaters. Roads are strewn with rubbish and stinking mud. "It reminds me of Banda Aceh after the tsunami," says Mr Handby.

He has been struck by the damaging force of the flood waters. "The velocity of the water and the type of construction used here means this flood has caused mass destruction. Many buildings have simply dissolved."

The Kabul River is still a raging torrent of brown water two weeks after the floods. Swaths of agricultural land remain inundated and some town streets are still knee-deep in putrid water. "There is just so much water with nowhere to go," Mr Handby says. "The frightening thing for me is this river has remained so high and we are still so early in the monsoon season."

With more rain forecast in northern Pakistan, locals fear further flooding. On Wednesday, the UN appealed for $US460 million ($A514.5 million) to provide immediate help, including shelter, food, clean water, sanitation and medical care.

The Pakistani government's response has been criticised by many as too slow and patchy, and Pakistan President Asif Ali Zardari visited the flood-affected areas for the first time last night.

Since going on his first Red Cross mission in 1984, Mr Handby has helped in many of the world's biggest humanitarian emergencies, including the Rwanda genocide, the Boxing Day tsunami, the Burma cyclone, Iraq and Kosovo.

For many years he combined short-term aid work with being an environmental health officer in local government. But three years ago the 60-year-old took a job as the water and sanitation co-ordinator for the Australian Red Cross's International Emergencies team. "It gives you an opportunity to achieve something for people who really need it," he says.

Mr Handby is planning what water and sanitation work the Red Cross and Red Crescent will do as they join many other humanitarian organisations in their emergency operations.

Many affected communities are without clean water so one of the first responses was to distribute chlorine tablets to allow families to purify water to drink. Now the race is on to provide more sustainable water supplies for flood-hit communities living in small tent cities that have sprung up on high ground.

Many communities along the river relied on open wells that have been contaminated by floodwater. Mr Handby is arranging for pumps to be bought so these can be drained of impurities. He also wants to cover open wells and install hand pumps that are not normally affected by flooding. He is working with local water authorities to try to get town water supplies functioning again.

But aid workers face many obstacles. The floodwaters surged through a well-stocked Pakistan Red Crescent storage depot near the town of Nowshera destroying much-needed relief supplies. Trucks at the depot are still stuck in the thick mud left behind.

Political instability and terrorism in north-western Pakistan is an added complication for aid workers.

Insurgents have threatened aid groups in the region and as a security precaution some agencies prevent their staff, especially foreigners, from being named in the media.